Update: Karpenter Introduction and Consolidation content refresh

[kuntshah]

What this PR does / why we need it:

Updated content in the Karpenter module of EKS Workshop:

Which issue(s) this PR fixes:

• index.md:
  Replaced the last two bullets describing what Karpenter does with a single, more accurate bullet:
  Before:
  "Scheduling the pods to run on the new nodes"
  "Removing the nodes when the nodes are no longer needed"

After:
"Disrupting the nodes when the nodes are no longer needed"

• consolidation.md :

  1. Expanded the description of consolidationPolicy options. The line about WhenEmpty now also mentions the Balanced option:

Before: "...set to WhenEmpty, which restricts disruption only to nodes that contain no workload pods."
After: "...set to WhenEmpty, which restricts disruption only to nodes that contain no workload pods or Balanced, when the cost savings outweigh the disruption to running pods."

2. Fixed an outdated policy name in the walkthrough intro:

Before: "...when disruption is set to consolidationPolicy: WhenUnderutilized"
After: "...when disruption is set to consolidationPolicy: WhenEmptyOrUnderutilized"
This aligns the prose with the actual policy value used earlier in the same file (WhenEmptyOrUnderutilized).

Quality checks

• My content adheres to the style guidelines
• I ran make test module="<module>" it was successful (see https://github.com/aws-samples/eks-workshop-v2/blob/main/docs/automated_tests.md)
• The PR has meaningful title and description of the changes that will be included in the workshop release notes

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[kuntshah]

I do not have access to check the logs for failure.